Synergistic metal sequestrant

ABSTRACT

MIXTURES OF TRIS(HYDROXYMETHYL)PHOSPHINE OXIDE, AND TRIS(N-ACETOAMINOMETHYL)PHOSPHINE AS WELL AS THE ALKALI MEETAL SALTS THEREOF, EXHIBIT MARKED SYNERGISM AS SEQUESTRANT COMPOSITIONS OVER A BROAD PH RANGE. THE SEQUESTRANT COMPOSITIONS ARE USEFUL AS ADDITIVES FOR DETERGENTS, METAL CLEANING BATHS, PEROXIDE COMPOSITIONS AND DYES. THE CHELATE PRODUCTS ARE USEFUL IN THE FIELD OF AGRICULTURE FOR THE INTRODUCTION OF TRACE ELEMENTS INTO PLANT LIFE AND ESPECIALLY IN THE TREATMENT OF IRON CHLOROSIS IN PLANTS.

United States Patent 3,836,556 SYNERGISTIC METAL SEQUESTRANT Ronald H.Carlson, Lewiston, N.Y., assignor to Hooker Chemical Corporation,Niagara Falls, N.Y.

No Drawing. Original application July 13, 1970, Ser. No. 54,663, nowPatent No. 3,734,861. Divided and this application Apr. 21, 1972, Ser.No. 246,489 The portion of the term of the patent subsequent to May 18,1988, has been disclaimed Int. Cl. Cd 9/02; A0111 7/00 US. Cl. 260-439 R3 Claims ABSTRACT OF THE DISCLOSURE RELATED APPLICATIONS This is adivision of application Ser. No. 54,663, filed July 13, 1970, now US.Pat. 3,734,861.

This application is a continuation-in-part of Ser. No. 680,011, filedNov. 2, 1967.

BACKGROUND OF THE INVENTION The invention relates to synergisticsequestrant mixtures, their use and the chelated products thereof.

The use of complexing agents which combine with metal ions in solutionto form Soluble complexes (which agents are commonly referred to assequestrants) is of great importance in many industrial processesinasmuch as it may prevent undesired precipitation reactions fromoccurring. For example, sequestration of calcium is important in watertreatment and in laundry solutions for controlling hardness of thewater. Sequestration of the heavy metals such as copper and nickel isessential in such areas as textile processing and metal cleaning andfinishing. Not all sequestrants, however, are equally eifective, theiractivity varying with their structures and the conditions under whichthey are used; for example, the common carboxylic acid sequestrants areoften ineffective in preventing ferric ion precipitation from alkalinesolutions of pH greater than 8.

The commercial utilization of water-soluble chelating compounds inagricultural applications to provide trace elements for plant growth iswell known. Likewise, the

treatment of plants suffering from chlorosis as a result of growth inalkaline soils devoid of sufiicient assimilatable iron is known. Variouschelating agents have been employed in the past to correct irondeficiencies in plants, the water solubiliity of chelated metal ionsafiords the primary route for potential assimilation into a plantstructure.

Ethylenediaminetetraacetie acid (EDTA) has been employed in the past fortreatment of iron deficiencies of citrus trees under acid conditions.The EDTA iron chelates are not stable in neutral and alkaline media. Thedevelopment of sequestrants which may be employed in acid media as wellas alkaline media is significant not only for agricultural applications,but for use in the detergent field, metal cleaning field, textile anddye industry and as stabilizers for organic and inorganic peroxides.

ice

SUMMARY OF THE INVENTION In accordance with the instant invention, thereis provided compositions of matter comprising tris(hydroxymethyl)phosphine oxide and a member selected from the group consisting oftris(N-acetoaminomethyl)phosphine, and the alkali metal salts thereof,in mole ratio of about 10/90 to /10.

'Furthermore, in accordance with the instant invention, there isprovided a process for sequestering metal ions from aqueous solutionover a pH range of about 4 to 10 by reacting the sequestrant mixture ofthis invention with metal ions.

Also, this invention provides novel compositions of matter comprisingthe sequestered metal ion derivatives of the sequestrant mixtures ofthis invention.

DETAILED DESCRIPTION OF THE INVENTION Mixtures oftris(hydroxymethyl)phosphine oxide (THPO) and tris(Nacetoaminomethyl)phosphine (TAM-P), and its alkali metal saltsunexpectedly display marked synergistic action as a sequestrantcomposition in mole ratios within the range from about 10/ 90 to 90/ 10,generally at a pH of from 4 to 10.

The metal ions which may be sequestered by the composition of thisinvention are those cations having a valence of two or more, such as theions of chromium, copper, nickel, tin, aluminum, cobalt, platinum,palladium, rhodium, iridium, ruthenium, osmium, zirconium hafnium, therare earths such as gadolinium, europium, neodymium, the actinides suchas uranium, and especially iron in the ferric (Fe+ state.

The tris(hydroxymethyl)phosphine oxide component of the synergisticsequestrant mixture need not be introduced into an aqueous system forcontaining metal cations as such, because it may be formed in situ inknown manner from various known precursors, such astris(hydroxymethyl)phosphine and tetrakis(hydroxymethyl)phosphoniumhalide. Generally, at a pH above 7, the tetrakis(hydroxymethyl)phosphonium salts are converted to the correspondingtris(hydroxymethyl)phosphine which undergoes oxidation to produce thephosphine oxide.

The tris(N-acetoaminomethyl)phosphine component of the sequestrantmixtures of this invention is preferably employed as its sodium (STAMP)or potassium (KTAMP) salt to increase water solubility.

The synergistic action of the sequestrant composition of this inventionvaries with the pH of the aqueous system as well as with the mole ratioof the components in the mixture. With mole ratios oftris(hydroxymethyl) phosphine oxide to tris(N-acetoaminomethyl)phosphinebetween 10/90 to 50/50, the synergistic sequestrant action toward theferric ion is evident at pH values from about 4 to 8, whereas with moleratios from about 50/50 to 90/10, the synergistic activity is extendedinto the pH range from about 7 to 9 and, with the 90/ 10 mole ratio ofreactants, into the pH 10 reg-ion.

The composition of this invention, when added to those solutions inwhich sequestration is desired, may be added as a solid or as asolution. If it is desired to add said composition as a solution, thecomposition may be dissolved in water. From about 0.001 percent to about50 percent concentration (by weight) may be used, though it is preferredto use from about 0.01) to about 5 percent concentration (by weight),and it is even more preferred to use from about 0.1 to about 3 percentconcentration (by weight).

It is preferred to use said compositions as sequestrants in aqueoussolutions. When said composition is added to the solution containingmetal ions to be sequestered, the temperature of said solution may befrom about 0 to about degrees centigrade, though it is preferred thatsaid temperature be from'about 20 to about 70 degrees centigrade, and itis even more preferred that said solution be at ambient temperature.

The sequestrant mixture of this invention may be formulated either as anaqueous solution containing the two components in the desired ratio oras a solid mixture.

The sequestered iron chelate may also be employed as an aqueous solutionor as a solid. The ferric iron chelate is soluble in aqueous alkalinesolution in an amount exceeding 20 percent by weight, and contains morethan 10 percent iron on a weight basis. Thus, when compared to theferric iron chelate of EDTA, which contains a relatively low percentageof iron, 5-10 percent by weight, and which exhibits low solubility inalkaline solution, the sequestrant mixture of this invention presentsdecided advantages.

The solid ferric (Fe+ iron chelates of this invention are of the generalcomposition in which n, x, y and z are numbers greater than 0, and maybe prepared by mixing apropriate amounts of ferric chloride, sodiumhydroxide, tris(hydroxymethyl)phosphine oxide (T-HPO) andtris(N-acetoaminomethyD- phosphine (TAMP) or a salt thereof in aqueoussolution. After the reaction is complete, the solid chelate may beforced from solution by addition of a lower alkanol, such as ethanol orisopropanol. The isolated chelate is then dried and ground into afree-flowing brown powder.

EXAMPLE 1 P(CH2NHCH2C OzNa); 4Hz0 NaCl HzCO Trisodium tris(Nacetatoaminomethyl)phosphine was prepared by the dropwise addition of 61grams of aqueous solution containing 29.92 grams (0.157 moles) ofdissolved tetrakis(hydroxymethyl)phosphonium chloride (THPC), withstirring, to 172 grams of an aqueous solution containing 34.45 grams(0.459 moles) of dissolved glycine at pH 11. During the addition ofTH-PC to the glycine solution, the pH of the reaction solution wasmaintained at pH 11 by the addition of 6 molar NaOH. An increase in thereaction solution temperature of 14 C. (from 25 to 39 C.) was observedduring the course of the THPC addition. A yellow-orange solution wasobtained upon completion of the THPC solution addition. The reactionsolution was stirred for an additional 45 minutes to ensure completereaction. Acetone was added to the aqueous reaction solution to obtain atwo phase system (an upper organic layer and a lower aqueous, oilylayer). The layers were separated by decantation and additional acetonewas added to the lower layer followed by successive decantations until asolid granular white mass was obtained. This material was vacuum driedover P at C. to yield a free-flowing white powder. Yield: 60.7 grams(100% of theory) Elemental analysis.-Calcd. for

P (CH NHCH CO Na) 3 H O (percent): P, 8.18; C, 28.50; H, 4.52; Na,18.20. Found (percent): P, 7.50; C, 28.99; H, 4.42; Na, 18.22. Theformation of STAMP was further suported by infrared and nuclear magneticresonance spectroscopic data.

EXAMPLE 2 Tris(N-acetoaminomethyl)phosphine is prepared by treating anaqueous solution of the trisodium salt with 3 equivalents of HCl to formthe protonated product.

EXAMPLE 3 The ferric (Fe+ iron chelate of THPO and STAMP is prepared byadding an aqueous solution containing tris(hyroxymethyl)phosphine oxideand trisodium tris- (N-acetatoaminomethyl)phosphine in the desired moleratio to an aqueous solution containing ferric ions. Sufiicient sodiumhydroxide is added to adjust the pH of the solution to 7. A clear,yellow to brown colored solution will form which is removed from anyprecipitated solid material by decantation. The solid ferric ironchelate is then forced from solution by the addition of a lower alkanol(ethanol, isopropanol, and the like) to the aqueous solution of thechelate to form a two-phase system. The phases are separated bydecantation and the lower chelate containing phase is evaporated todryness in vacum at an elevated temperature (about 50 C.). After drying,a finely divided, free-flowing powder is obtained.

EXAMPLE 4 The sequestering efficiency of the sequestrant mixtures ofthis invention as well as the individual sequestrants were determined bytitrating an aqueous solution 0.5 molar in FeCl dropwise into a stirred50 gram aqueous solution containing 0.5 gram of dissolved sequestrantuntil the end point was reached as observed by a perceptible permanenthaze in the solution. The pH of the solution of dissolved sequestrantwas initially adjusted to the desired point and maintained at thespecified pH during the titration by addition of aqueous sodiumhydroxide as needed to control the hydrogen ion concentration.

The sequestering efliciency was then calculated in terms of the poundsof ferric ion sequestered per 100' pounds of sequestrant. A sequesteringefficiency designation of 1.00 represents 7.1 pounds of ferric ionsequestered by 100 pounds of sequestrant.

The data presented in Table I compare the sequestering efiiciency oftris(hydroxymethyl)phosphine oxide (THPO) and trisodiumtris(N-acetatoaminomethyl)- phosphine (STAMP) and mixtures of these twosequestrants in the ratios indicated at the stated pH, for ferric ion.The mole ratio of the components of the synergistic sequestrant mixtureis within the range from 10/90 to 10.

TABLE I THPO/STAMP THPO Stamp 10/90 511/50 530/10 It is clear from thedata presented in Table I that mixtures of tris(hydroxymethyl)phosphineoxide and trisodium tris(N-acetatoaminomethyl)phosphine exhibitsynergistic activity in the sequestration of the ferric ion at a pHvalue from about 7-8 for the compound mixtures in mole ratio from about10/ 90 to 90/10, while at pH values from about 4-7, the synergisticactivity is found in the mole ratio range from about 10/90 to 50/50, andat pH- values from about 8-9 the synergistic activity is exhibited inthe mole ratio range from 50/50 to 90/ 10, extending in the 90/ 10mixture to a pH value of about 10.

To further place the instant invention in perspective, the sequesteringefiiciencies of several known sequestrants for the ferric ion arepresented in Table II. The abbreviations employed are as follows:

Trisodium nitrilotriacetate-SNTA Disodium imin0diacetateSIDA SodiumtripolyphosphateS'I-PP Tetrasodiurn ethylenediaminetetraacetateAEDTAGluconic acid Trisodium hydroxyethylethylenediaminetriacetate- SHEDTAPentasodium nitrilotrimethylene phosphonate-SNTMP Pentasodiumdiethylenetriaminepentaacetate-SDTPA.

TABLE II sequestering efficiency Scquestrant pH4 pH5 pH6 pH7 p118 p119pHlO pHll pH12 From a comparison of the sequestering efliciencies of theknown sequestrants presented in Table II, with the synergisticsequestrant mixture THPO/ STAMP presented in Table I, it is apparentthat the mixed sequestrant of the instant invention provides completelyunexpected activity toward the ferric ion.

What is claimed is:

1. An iron chelate compound prepared by reacting a mixture oftris(hydroxymethyl)phosphine oxide and a member of the group consistingof tris(N-acetoaminomethyl) phosphine and an alkali metal salts thereofin mole ratio of about 10/90 to 90/10 with ferric ions in aqueoussolution at a pH from about 4-10, and thereafter recovering said ironchelate compound as a solid product.

2. An iron chelate compound as recited in claim 1 prepared by reacting amixture of tris (hydroxymethyl) phosphine oxide and a member of thegroup consisting of tris(N-acetoaminomethyl)phosphine and an alkalimetal salt thereof in a mole ratio of about 10/90 to 50/50 with ferricions in an aqueous solution at a pH from about 48.

3. An iron chelate compound as recited in the claim 1 prepared byreacting a mixture of tris(hydroxymethyl) phosphine oxide and a memberof the group consisting of tris(acetoaminomethyl)phosphine and an alkalimetal salt thereof in a mole ratio of about /50 to 10 with ferric ionsin an aqueous solution at a pH from about 7-9.

References Cited UNITED STATES PATENTS LEON D. ROSDOL, Primary ExaminerD. L. ALBRECHT, Assistant Examiner US. Cl. X.R.

71-], Digest 2; 252

